The letter used in some operating systems, including DOS, Windows and IBM's OS/2 to denote the hard disk drive on the system. Normally a PC has two or three disk drives within its casing. One floppy disk, called A: and one hard disk called C:. If you have a second floppy disk, this is called B: and a CD-ROM drive is normally D:. When talking about the different disk drives, you say 'drive C' for the hard disk, but normally write 'C:'. If you are using DOS, when your PC starts up it will normally show what's called the C prompt, which looks like 'C:\>' on your screen. This means you are currently looking at the hard disk. (See also floppy disk, hard disk.)
